Bleb morphology of glaucoma drainage devices on magnetic resonance imaging

Purpose: To evaluate bleb morphology features of different glaucoma drainage devices (GDD) using magnetic resonance imaging (MRI). Materials and Methods: Prospective cohort study of GDD and bleb morphology in consecutive glaucoma patients implanted with Ahmed Glaucoma Valve (AGV), Paul Glaucoma Implant (PGI), Baerveldt Glaucoma Implant (BGI) and Ahmed ClearPath (ACP) devices. Thirty-six eyes from 30 consecutive patients underwent standardized GDD implantation followed by MRI at least 1 month after surgery. Main outcomes included bleb volume and endplate position relative to the optic nerve. Secondary outcomes included intraocular pressure (IOP), medication and surgical complications during a 12-month follow-up. Results: Seven eyes were implanted with the AGV (19%), 5 with BGI (14%), 16 with PGI (44%) and 8 with ACP (22%). MRI scans were obtained 85 +/- 66 days after surgery. Mean total bleb volume was 563 +/- 390 mm(3). This bleb volume was inversely correlated with early post-operative IOP (day 7; r(s) = - 0.3326, p = 0.0475) but positively correlated with IOP at 12 months (r(s) = 0.3592, p = 0.0341). No significant difference in total bleb volume was found between GDD types (p = 0.1223). A double-layered bleb was observed in 34 eyes (94%). The inferior bleb volume was significantly larger in PGI devices versus other GDD types (380 +/- 205 vs. 193 +/- 161 mm(3); p = 0.0043). Distance from the endplate to the optic nerve was 9.5 +/- 4.0 mm, similar across GDDs (p = 0.2519). Conclusions: Double-layered blebs are a common finding with GDDs. Bleb volume showed different correlations with IOP at distinct timepoints and the PGI device formed larger blebs. A standardized GDD implantation technique ensures a safe distance from the GDD endplate to the optic nerve.